Su-27 Flight Model Discussion

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You'd better not missclick the update invite as soon as you launch DCS ;)

I've been known to do that. :)

Guys if someone tried to fly stable backstroke like in this picture?

I tried. It's confirmed stable for a few seconds ;)

Then the kerosene doesn't want to jump into the engines.

I can't remember where I've read that, but the inverted flight can only be sustained during 8 to 15 seconds. Something like that.

If I find the line about the fuel system and tank design, I'll post it here.

[edit: more precisely:

22. Полет с околонулевыми и отрицательными перегрузками (Пу = 0 ÷ -2) разрешается:

− на форсажных режимах работы двигателей не более 3 сек. на высотах до 15000 м, не более 8 сек. на высотах более 15000 м;

− на бесфорсажных режимах работы двигателей не более 10 сек. на высотах до 8000 м, не более 15 сек. на высотах более 8000 м.

Повторное создание указанных перегрузок разрешается не ранее, чем через 30 сек. полета с Пу ≥ 1,0. Полеты с перегрузкой Пу = 2 ÷ -2 выполнять при остатке топлива более 1500 кг.

(partial translation below)

[-2 to 0 G flight duration:]

 

- with afterburners: a maximum of 3 seconds at altitudes up to 15,000 meters, and a maximum of 8 seconds at altitudes above 15,000 meters;

- without afterburners: a maximum of 10 seconds at altitudes up to 8000 meters, and a maximum of 15 seconds at altitudes above 8000 meters.

Su-27SK Flight Manual, again (what would we do without it?) ;)

And I hope that was what you were wondering about.]

And I hope that was what you were wondering about.]

Absolutely. Thank you! :thumbup:

Flaps in the Su-27 extend automatically if you're slow enough or AoA is high enough. Just like the slats. The flaps don't extend fully though unless you command them to.

this no happens with new pfm physics. with old physics that work fine

and if u watching the stream u can see the Wags flying around 750+ Kph and with FLAPS ON and he was flying at level at that time.

this no happens with new pfm physics. with old physics that work fine

 

and if u watching the stream u can see the Wags flying around 750+ Kph and with FLAPS ON and he was flying at level at that time.

how are you coming to the conclusion that flaps were down from the inside of the cockpit?

lemme watch stream again and look for the flaps indicator... which he RARELY looked down at.

how are you coming to the conclusion that flaps were down from the inside of the cockpit?

 

lemme watch stream again and look for the flaps indicator... which he RARELY looked down at.

This is OT so should probably be moved to the Su-27 sub-forum but I tried this and the flaps do stay down at high speeds, even excess of 1000 kph.

Yeah if your flaps go down, they wont go up again automatically.

I think EAK is confusing flaps with slats on the leading edges of the wings, which operate automatically depending on the AoA.

I think EAK is confusing flaps with slats on the leading edges of the wings, which operate automatically depending on the AoA.

That should be causing damage IMHO.

ok, so where do you see the flaps indicator showing them down...?

with them down at high speed, youd have damage as well as increased drag and trim issues.

ok, so where do you see the flaps indicator showing them down...?

 

with them down at high speed, youd have damage as well as increased drag and trim issues.

You get trim issues, damage you don't.

If the flaps jam down, that's damage.

If the flaps are jammed down, they cause trim issues...

you can get them up again, they just dont go up automatically, as you speed up.

That should be causing damage IMHO.

So should pulling 80G's to dodge my slammers :music_whistling:

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Second I apologize, looks like you can invert depart even with ASC disabled however I had to abuse the aircraft to do so and is most apparent at high altitudes.

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It's in fact just as easy as keeping the stick full forward with the FBW active if the speed falls below some value or if you have flaps deployed. Just push the stick full and at about 1-2 seconds you depart.

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-CG playing back and forth with fuel status. It was in discussion on another thread which with a pure shameless and abusive action has been re-titled as "NO BUG". Maybe someone else (because I'm sick of this already) will take the time to investigate this issue better than me.

So why is it that you feel the cg shouldn’t shift back and forth depending on fuel state? Have you taken the time to read the real world manual to learn the quantity of fuel and sequence in which that quantity is drawn from the four tanks and reserve tank?

The problem is that you have not taken the time to quantify your observations and now you say you’re sick of wasting your time. I was in the process of quantifying this aspect (cg shift) for you but, now, if you don’t care, why should I?

OnlyforDCS,

His flights were made under direct control.

Thanks for the reply Ironhand

Ironhand where did you get the info on the tanks? I reread the Su-27 manual by ED after your post but didn’t see anything about the sequence of fuel tank depletion. The only indication are the individual fuel tanks lights on the fuel indicator, and I(like a lot of people on the English forums) can’t read cryllic. I looked up the Su-27SK manual but not only is it hard find, it seems to all be in cryllic.

Long time lurker and Flanker fan since Lock On days

This is the internal fuel overlay:

And this is the consumption sequence:

FOR A FULL LOAD OF FUEL:

1º.- 1720 Kg from tank Nº1

2º.- Tank Nº4 completely.

3º.- Tank Nº1 (rest ) completely.

4º.- 70 Kg from tank Nº2

5º.- Tank Nº3 ( both symetric ) completely.

6º.- 3210 kg from tank Nº2 ( except the content of the central feeder )

7º.- The rest of the Tank Nº2 completely.

lol, if you've ever played Kerbal Space Program, you know the order tanks drain is very important :D

That's surprisingly detailed and specific info, though. Cool.

This is the internal fuel overlay:

 

And this is the consumption sequence:

 

FOR A FULL LOAD OF FUEL:

 

1º.- 1720 Kg from tank Nº1

2º.- Tank Nº4 completely.

3º.- Tank Nº1 (rest ) completely.

4º.- 70 Kg from tank Nº2

5º.- Tank Nº3 ( both symetric ) completely.

6º.- 3210 kg from tank Nº2 ( except the content of the central feeder )

7º.- The rest of the Tank Nº2 completely.

Very useful, thanks for posting that.

IIRC the capacity of the cache tank is 500 Kg.

Very useful, thanks for posting that.

 

IIRC the capacity of the cache tank is 500 Kg.

600 kg. And for clarity, Esac_mirmidon's No 7 in the sequence is the cache/feeder tank which is a part of tank #2.

Also, that sequence is specifically for the nonafterburning regimen. Afterburning mode and emergency fuel dump are different, though the manual isn't specific about how. It simply makes the distinction and then speaks in generalities about the latter. For that reason, the data I was gathering was generated under full military power rather than afterburner.

AeriaGloria,

There's an English Google (?) translated version of it floating around out there as well, though it leaves a lot to be desired. Also an excellent Spanish version. That one's yours, isn't it Esac_mirmidon?

Esac_mirmidon, thank you for the diagram and response, very helpful